(1) Field of the Invention
The invention relates to a method for controlling high condenser pressure in an air conditioning unit.
(2) Description of the Related Art
In most air conditioning unit systems, there is established a high pressure set point. When the internal pressure of the refrigerant within the air conditioning unit exceeds the set point, such a system customarily shuts down. In fact, there is commonly established a fixed high pressure differential threshold. This differential threshold provides a safety buffer so as to prevent the actual pressure and inside of an air conditioning unit from ever reaching the high pressure set point. In such a scenario, when the internal condenser pressure of the air conditioning unit reaches the high pressure set point minus the fixed high pressure differential threshold, the system is shutdown. In addition, as cooling capacity is added to such an air conditioning unit, additional capacity will not be added if the internal pressure within the air conditioning unit is greater than the high pressure set point minus the fixed high pressure differential threshold, even if increasing capacity under such a condition would not cause the pressure in the air conditioning unit to exceed the high pressure set point.
There therefore arises two potential problems when determining the high pressure differential set point. The first arises from the possibility of setting the fixed high pressure differential set point too high. If the fixed high pressure differential set point, equal to the high pressure set point minus a high pressure differential, then it is possible that bringing an additional compressor on line in a situation wherein the current discharge pressure of the system is below the fixed high pressure differential set point will cause the discharge pressure to rise to a point greater than the high pressure set point. In such an instance, the system will be forced to shutdown. Conversely, setting the high pressure differential set point too low may prevent the air conditioning unit system from increasing capacity even though increased capacity loading is both required and possible.
What is therefore needed is a method of setting a fixed high pressure differential set point such that an air conditioning unit is prevented from tripping at high pressure failure when additional capacity is brought on line, and wherein capacity unloading occurs in an efficient manner when the discharge pressure of the air conditioning unit reaches the high pressure set point of the system.